Use of liquefied gas as a fuel source for various applications has gained popularity in recent years due to the lower cost and cleaner burning of gaseous fuels such as liquefied petroleum gas (LPG), compressed natural gas (CNG), or liquefied natural gas (LNG), as compared to more traditional fuels such as gasoline or diesel. In practical applications, for example, mining trucks, locomotives, highway trucks and the like, to gain sufficient range between refueling, the gaseous fuel is stored and carried on-board the vehicle in a liquefied, pressurized, cryogenic state.
Some applications require the handling, and more particularly the pumping, of cryogenic liquids. For example, heavy machines like locomotives or large mining trucks may have engines that use more than one fuel. The engine may be a dual fuel engine system, in which a gaseous fuel, such as compressed natural gas, is injected into a cylinder at high pressure while combustion in the cylinder from an ignition source, such as a diesel pilot, is already underway. With such engines, the fuel may be stored at low, cryogenic temperatures and relatively high pressures in a storage tank in order to achieve a higher storage density, and vaporized into a gaseous form by a heat exchanger before it is introduced into the engine. However, the use of such a cryogenic fuel requires the use of specialized equipment, including a cryogenic tank for storing the liquefied natural gas (“LNG”) fuel and a cryogenic pump for withdrawing and pressurizing the liquefied natural gas fuel.
U.S. Pat. No. 4,443,160 (“the '160 patent”) describes one example of a high-pressure pump for liquids. More specifically, the '160 patent describes using pressure in a piston/tappet assembly to adjust the angle of a swash plate. The arrangement described in the '160 patent as well as other traditional arrangements for drive systems for high pressure pumps used in the types of applications describe above involve complicated bearing assemblies and load plates that expose the components to wear and add to the size of the overall pump. Additionally, pumps like those described above often include various external components, such as oil tanks and pumps, to provide lubrication to the internal components of the pump. These external components add to the space required to use the pump and add complexity to the pump system.